Viruses of the Flavivirus genus are positive-sense, single-stranded RNA viruses of the Flaviviridae family, many of which are responsible for disease in humans and other mammals. Examples of flaviviruses include Tick-borne encephalitis virus, Japanese encephalitis virus, Yellow Fever virus, St. Louis encephalitis virus, hepatitis C virus, and West Nile viruses. Flaviviruses of the Flavivirus genus generally comprise three major mature structural proteins: an envelope (E) protein, a capsid (C) protein, and a membrane (M) protein. The M protein is usually formed as a proteolytic fragment of a pre-membrane (prM) protein. See, e.g., FIELDS VIROLOGY 997-998, Raven Press, Ltd., New York (D. M. Knipe et al. eds., 4th ed., 2001), 996 (hereinafter “FIELDS VIROLOGY”), and the ENCYCLOPEDIA OF VIROLOGY (R. G. Webster et al. eds., Academic Press, 2nd ed., 1999), each of which is incorporated herein by reference in its entirety for all purposes.
Dengue (DEN) viruses are known among flaviviruses as agents of disease in humans. Dengue viruses comprise four known distinct, but antigenically related serotypes, named Dengue-1 (DEN-1 or Den-1), Dengue-2 (DEN-2 or Den-2), Dengue-3 (DEN-3 or Den-3), and Dengue-4 (DEN-4 or Den-4). Dengue virus particles are typically spherical and include a dense core surrounded by a lipid bilayer. FIELDS VIROLOGY, supra.
The genome of a dengue virus, like other flaviviruses, typically comprises a single-stranded positive RNA polynucleotide. FIELDS VIROLOGY, supra, at 997. The genomic RNA serves as the messenger RNA for translation of one long open reading frame (ORF) as a large polyprotein, which is processed co-translationally and post-translationally by cellular proteases and a virally encoded protease into a number of protein products. Id. Such products include structural proteins and non-structural proteins. A portion of the N-terminal of the genome encodes the structural proteins—the C protein, prM (pre-membrane) protein, and E protein—in the following order: C-prM-E. Id. at 998. The C-terminus of the C protein includes a hydrophobic domain that functions as a signal sequence for translocation of the prM protein into the lumen of the endoplasmic reticulum. Id. at 998-999. The prM protein is subsequently cleaved to form the structural M protein, a small structural protein derived from the C-terminal portion of prM, and the predominantly hydrophilic N-terminal “pr” segment, which is secreted into the extracellular medium. Id. at 999. The E protein is a membrane protein, the C-terminal portion of which includes transmembrane domains that anchor the E protein to the cell membrane and act as signal sequence for translocation of non-structural proteins. Id. The E protein is the major surface protein of the virus particle and is believed to be the most immunogenic component of the viral particle. The E protein likely interacts with viral receptors, and antibodies that neutralize infectivity of the virus usually recognize the E protein. Id. at 996. The M and E proteins have C-terminal membrane spanning segments that serve to anchor these proteins to the membrane. Id. at 998.
Dengue viruses are primarily transmitted to humans through the mosquito Aedes aegypti. There is a significant threat of dengue infection to people living in or visiting tropical areas. Indeed, an estimated 2.5 billion people live in areas at risk for transmission and over 100 million humans are infected each year. Infection with dengue virus is estimated to kill approximately 20-25,000 children each year.
An initial dengue virus infection is clinically manifested for most of the cases by dengue fever (DF), which is a self-limited fibril illness. Although rarely fatal, DF is characterized by often-severe disseminated body pain, headache, fever, rash, lymphadenopathy and leukopenia. Subsequent infection with a heterologous Dengue virus can lead to the much more severe to fatal disease of dengue hemorrhagic fever (DHF) or dengue shock syndrome (DSS). It is hypothesized that the presence of antibodies to the serotype causing the primary infection enhances the infection by a heterologous serotype in secondary infections. This phenomenon is referred to as antibody-dependent enhancement (ADE) of the disease.
Effective diagnosis of dengue virus is often problematic. All four dengue virus serotypes can be prevalent in one local area and it is therefore important to test a subject's serum samples simultaneously against all 4 dengue virus serotypes.
There is currently no specific treatment for dengue virus infections. Although the development of dengue virus vaccines has been ongoing for the past 50 years, no successful vaccine to dengue virus has been produced and no licensed dengue virus vaccine is yet available. A major challenge is to generate a tetravalent vaccine that induces neutralizing antibodies against all four strains of dengue to avoid ADE when the individual encounters viruses of two or more different serotypes. Vaccine strategies using a mixture of DEN 1-4 attenuated viruses have been largely unsuccessful, because the antigens from one type will tend to dominate or “mask” the others, producing an incomplete immune response across the four types.
There remains a need for molecules, compositions and methods for effectively diagnosing one or more dengue viruses, inducing, enhancing, or promoting an immune response to flaviviruses, particularly dengue viruses, and preferably to all four dengue virus serotypes, and prophylactically or therapeutically treating disorders or diseases related to one or more such viruses. The present invention provides such molecules, methods and compositions. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.